With the option to 'Allow Adobe to install updates', the update will be automatic. Without that setting enabled, either install the update via the update mechanism when prompted or via the Download Center*.

*Important Note: Downloading the update from the Adobe Flash Player Download Center link includes a pre-checked option to install unnecessary extras, such as McAfee Scan Plus or Google Drive. If you use the download center, uncheck any unnecessary extras that you do not want. They are not needed for the Flash Player update.